This invention relates to electronic display driving apparatus and, more specifically to a circuit arrangement for driving an external electrode gas discharge display panel (usually called a plasma display panel) in a time division fashion.
A plasma display panel generally comprises a stack of three thin flat glass or transparent dielectric plates. The central plate is provided with a plurality of perforations at predetermined locations. The periphery of the stack is hermetically sealed. The internal voids within the stack are evacuated and then filled with neon or a similar inert gas or mixture of gases. On one surface of each of the outer plates, there is disposed the so-called matrix electrodes which consist of rows and columns of electrodes perpendicularly spacially intersecting one another with the perforations, i.e., the gas-filled voids, interposed therebetween. The matrix electrodes crossing at each of the selected perforations which correspond to a letter or symbol to be displayed are selectively supplied with high-frequency pulses whereby a gas discharge is caused in the selected perforations to display the desired letter or symbol. In one improvement for such conventional plasma display panels constructed as above described, two thick glass or transparent dielectric plates are used as the outer plates and provided with thin glass or other dielectric films on their inside surfaces, respectively. Further, a plasma display panel having no central plate, and a plasma display panel in which segmented type electrodes are substituted for the matrix electrodes, have been proposed.
In any of the conventional panels, discharge occurs in a gas space (herein called a gas discharge cell) identified by a pair of opposing external electrodes which are selectively supplied with a direct current voltage higher than the firing voltage V.sub.f of the cell (with the voltage drop across the dielectric plates being neglected). Once discharge occurs in a cell, charged particles generated by the discharge charge the dielectric plates to reduce the strength of the electric field within the cell until the discharge ceases when the sum of the supplied voltage and the reverse voltage resulting from the charges stored on the dielectric plates falls below the discharge sustaining voltage V.sub.s of the cell. The time interval between occurrence of the discharge and termination thereof is from scores to several hundreds of nanoseconds. When the polarity of the direct current voltage supplied between the opposing external elecrtrodes is reversed to be of the same polarity as the voltage resulting from the stored charge, the voltages applied across the cell are superimposed on each other to become sufficiently higher than the firing voltage V.sub.f. Thereupon, the discharge starts again until it eventually ceases. By repeating the procedure, namely, by applying a voltage of alternating or successively reversed polarity between the opposing external electrodes, it is possible to sustain the intermittent discharge. If the frequency of repetition of the intermittent discharge per unit time is appropriately selected (for example, 5 kHz), it is possible to provide a display of sufficient brightness.
A preferred conventional circuit arrangement for driving a plasma display panel comprises means responsive to a d.c. voltage at least equal to the unidirectional firing voltage V.sub.uf of the panel, high-frequency or clock pulses, and each of first address pulses specifying respective ones of the first electrodes of the panel, which may be the row electrodes, or supplying unidirectional pulses of a pulse height at least equal to the unidirectional firing voltage V.sub.uf and of the pulse repetition frequency of the clock pulses to the first electrode specified by the above-mentioned first address pulses. The circuit arrangement further comprises means comprising, in turn, variable impedance elements adapted for connection to respective ones of the second electrodes of the panel, which may be the column electrodes, and rendered on in accordance with respective ones of second address pulses specifying the respective second electrodes to prevent pulses from being derived at the second electrode specified by each of the second address pulses through the electrostatic coupling which is present between the first and second electrodes within the panel.
As will later be described in detail with reference to the accompanying drawing, it is necessary to use switching elements capable of withstanding a high voltage and a plurality of AND gates in the unidirectional pulse supplying means of the preferred conventional circuit arrangement. This has rendered the prior art conventional circuit arrangement expensive and complicated.